A diesel engine achieves combustion by injecting fuel that vaporizes into the hot air of an engine cylinder. However, during cold starting conditions, the air loses much of its heat to the cylinder walls making engine starting difficult. For example, if too much fuel is injected into the cylinder, the heat required to vaporize the cold fuel reduces the air temperature about the injection point and may prevent or quench combustion. Thus, it is desirable to inject fuel slowly to disperse the fuel throughout the combustion chamber to evenly distribute the resulting heat losses in order to cause combustion.
The injection rate of hydraulically-actuated fuel injector systems, similar to those described in U.S. Pat. Nos. 5,191,867 and 5,181,494, is controlled by the actuating fluid pressure and viscosity. However, the fluid viscosity changes in response to fluid temperature and fluid grades. Although it is possible to control the actuating fluid pressure as a function of fluid temperature for a single fluid grade, it becomes increasingly difficult to control the actuating fluid pressure to start an engine where the fluid grade is unknown.
The present invention is directed to overcoming one or more of the problems as set forth above.